This field of invention is related, but not limited to, the automobile industry. In particular, the field relates to mechanical engines and large-scale mechanical devices that utilize motile lubricating fluids operating in high temperature environments. For these lubricants, it would be beneficial to monitor in real-time the changing fluid properties, the levels of contaminants, and changes in performance to ensure safe and reliable operation of the equipment being protected by the lubricating system. This approach applies to automotive vehicles, aircraft or spacecraft, industrial equipment, wind-turbines, life-saving medical machinery and other critical devices. The conditions of fluids are often detected using a static, periodic approach, typically requiring removing fluid from the system, often by extracting a sample of the fluid to send to testing laboratories around the world, which have established procedures and methods to measure a number of aspects of the lubricating fluid, including historical time-series of various parameters. It is common practice to apply such time-based longitudinal monitoring of the fluid to detect changes over time to gain an understanding of the changes in performance within the closed environment. For example, the presence of specific particles at increasing concentrations can indicate levels of wear and performance of certain underlying components within the system being lubricated. This testing typically measures changes in characteristics of the fluid over time, including detecting changes and deterioration of underlying lubricating fluid and additives and the detection of normal (expected) and abnormal (unexpected) “wear” of the moving parts due to normal operation. Static samples are usually sent to a facility that performs a number of tests, including detecting the presence of foreign materials and objects. In some cases, such as when the lubrication fluid is changed, the lubrication filter is commonly sent as well as the oil for testing and detailed analysis. For both the sample and the filter, this is a destructive “tear down” analysis—such that the filter and the sample are not returned to service, but evaluated and subsequently removed. Tests typically performed in the laboratory include detection of metallic and non-metallic particles, presence of water or other non-lubricant liquids, carbon soot and other components, and in some cases, verification that the underlying chemistry of the lubricant is still intact. A written (or electronic) report is generated and transmitted to the stakeholder upon completion of the testing. Results typically take days or weeks from extraction to stakeholder review.
A number of low-cost lubricating fluid measurement products and techniques are emerging onto the market—including a consumer static “check” of a motor oil sample (see lubricheck.com) which measures the changes in electrical impedance characteristics (electrical capacitance and resistance when a small electrical source is applied across the sensor where a sufficient sample size of the lubricant bridges the sensor electrode across to the detector). This approach performs a single-dimensional measurement of oil sump fluid properties at a point in time in the evolution of the oil (i.e. a static measurement), providing insight only when the operator manually extracts a sample of oil to be tested and only indicates changes in the electrical properties should the data be appropriately logged and tracked over time. This approach has many drawbacks including the interval sampling (only when the operator makes a measurement), as well as the potential for counteracting forces from the presence of multiple contaminants introduced into the fluid to mask the true state/condition of the lubricant. As an example, in the case of an automobile engine, the normal operation of the combustion engine will produce carbon by-products as a result of the operation of the engine (this is what discolors the oil). If a vehicle were producing only this carbon “soot” the resistance would change (increase) due to the introduction of the soot. If at the same time, the engine were undergoing adverse ‘wear’ to the extent that small metallic particles were produced as an abnormal condition across the internal moving parts, these particles would decrease the resistance, as metal is a better conductor over the base lubricant. In the case where both soot and metallic particles were being produced at the same time, they could partially or completely cancel out some or all the measurable effects—thus providing a false indication of the true condition of the lubricant and underlying engine. A testing laboratory analysis by comparison performs a number of tests which would be able to independently detect the presence of both materials in the base lubricant fluid and provide an accurate report of the condition of the fluid and the resulting system.
Lubricating fluids have to accommodate a wide range of operating conditions—including variances in temperature, pressure, purity, and state change. Lubricants are often optimized for a specific operating environment and temperature range and are expressed in viscosity. Some lubricants are designed to operate with multiple viscosities (e.g., 10W-30 multi-grade viscosity motor oil). Typically, measurement of the fluid condition and properties is static and performed externally outside this operating environment via sampling when in a static/non-operating state. Static sampling does not necessarily validate the condition of the fluid in the operating state—either within or outside the normal/typical operating range. There are expensive and complex sensors that have been developed for measuring lubricating fluid and other liquids in real time—either for use in laboratory environments and conditions or for very high-value machinery where immediate sensor lubrication information is critical. Companies such as Voelker Sensors, Inc. offer a product for the machine tool industry that measures in real time a number of parameters including oil level, oxidation (change in pH), temperature, etc. The sensor element is not MEMS based and has a larger footprint, and is not suitable in size/form factor for operation within automobile oil/lubrication systems (“Continuous Oil Condition Monitoring for machine Tool and Industrial Processing Equipment,” Practicing Oil Analysis (9/2003).
Outside of the field of integrated-circuit multimodal sensor systems, there have been various implementations of continuous electrical property measurements as performed by Halalay (U.S. Pat. Nos. 7,835,875, 6,922,064, 7,362,110), Freese et al., (U.S. Pat. No. 5,604,441), Ismail et al., (U.S. Pat. No. 6,557,396), Steininger (U.S. Pat. No. 4,224,154), Marszalek (U.S. Pat. No. 6,268,737), and others which disclose either a singular vector analysis (electrical) or a time series measurement of electrical properties to derive an understanding of the oil condition. The challenge remains, as in the Lubricheck approach, to overcome the interdependent and true measurement cancelling effects that can report an incorrect oil condition. This is precisely why the fluid testing protocols and laboratories apply tests across multiple dimensions to include spectral analysis as well as tests to determine metal and other foreign object content in the oil samples.
Lubricants are designed to perform beyond their stated range and are further enhanced through the addition of “additives” to extend the lifetime and safety margin of the fluid. Understanding the lubrication longevity is crucial for the safe operation of the system. Replacement of the fluid is performed typically at very conservative (i.e. short) recommended intervals, providing a wide safety margin for the operator. In general, lubricants can operate for significantly longer intervals, or in the case of specific equipment operating in harsh environments (e.g. military equipment used on the battlefield or in mining operations, etc.) may require a more aggressive replacement cycle. It is important to determine when the lubricating fluid cannot continue to perform according to specifications determined by the equipment/system manufacturers. As long as the lubricating fluid is within the safe margin of operation, it may operate indefinitely and not need to be exchanged or replaced with fresh lubricating fluid.
Providing a more precise measure of the fluid's performance can maximize the lifetime of both the lubricant and the equipment the lubricant is protecting. As the cost of the equipment and the hydrocarbon lubricant increase, so does the value of providing both a longer and more precise lifetime of the lubricant and early detection and notification of pending equipment performance deterioration (including motor, filter, and other components in the system, etc.). This approach can potentially save lives when critical equipment failures are detected in advance. In addition, should the fluid fail and contribute to the equipment breaking down, this system potentially eliminates the resources required and time lost to repair/replace the underlying/broken equipment. This approach also avoids the loss of service and resources required to complete oil changes more often than actually needed.